Your friend are correct. It's just region build. But region build is for region AND carrier request, and some minor bugs and process are different. So even with same build date, you might find one better than another.

7.Dec:
- Update to I9250XWKK9 same ITL41F , build date 29.November.2011
25.Dec
- Merry Christmas. I9250XWKL2 ICL53F
Hi,
Here is i9250XWKK8 firmware with XXKK1 radio.
Build date: 24.Nov.2011 11:41:32 KST (From build.prop)
PDA Build: ITL41F
It's NOT the ITL41F that you guys are using. You guys using is XX , while this one is XW .
I, myself was using this one since 25.Nov till few days ago and confirm that it fixed volume problem, and for me, this XW is lots more stable and battery is better than XX version. (Well, don't ask me why I said "till few days ago. I'm still with XW, but on newer December version) Ah, you can use with XXKK6 radio as well. No problem at all.
CAUTION: (PLEASE, I BEG YOU SPEND FEW MINUTES TO READ IT AT LEAST TWICE)
- READ THIS. READ THIS. READ THIS.
- BACKUP your internal storage. BACKUP your internal storage.
- Package contains bootloader, please don't flash it if you don't know what it for.
- Flash to this will completely delete all your internal storage. So backup with CWM, backup with Titanium, and copy to your PC before flash.
- Make sure battery is at least 50%
- Make sure do NOT unplug your phone while it flashing.
(Bla bla bla........ ya ya, I know I know you guys is not amatuer).
Link:
- ODIN and partition file
http://www.filesonic...file/4116481164
- i9250XWKK8
Part 1 : 100 MB (104,857,600 bytes) http://www.filesonic...file/4103908124
Part 2 : 67.1 MB (70,444,481 bytes) http://www.filesonic...file/4103908134
-i9250XXKK9
Part 1 : 100MB (104,857,600 bytes) http://www.filesonic...file/4116445734
Part 2 : 62.4MB (65,437,696 bytes) http://www.filesonic...file/4116445774
-i9250XWKL2
Part 1 : 95.7 MB (100,431,872 bytes) http://www.megaupload.com/?d=CBWO5EO2
Part 2 : 69.6 MB (73,061,991 bytes) http://www.megaupload.com/?d=IY1QG55Z

Try hold vol down + power on then connect usb cable and check if pc able to detect the phone? If yes then easy to fix.
If not then I recommend you try another usb port / another PC, if still no good news then warranty is what you need to consider.

confirm the alternative way working. And it's easiest.
Add: have to turn on 1-click setting on mobile:
try to purchase any free app, then it will ask for that, just click the link,put ANY mobile number with +1 like +17537483535 then press turn on and done :D